The present invention relates to a device for manufacturing concrete parts, particularly tubular parts in a sinking mold of the type which includes an upright holding fixture, preferably in the form of a central vibrator, secured to a stationary support, a mold core releasably mounted on the holding fixture, a mold jacket, a molding bottom ring and means for supplying concrete material.
In a known manufacturing device of this kind operating with sinking mold jacket or rising mold core it is possible to produce concrete pipes, and also steel concrete pipes provided with a reinforcing wire mesh. If the device is operated according to the method of a rising mold core, very deep underfloor pits are necessary. If instead it is operated according to the known method of a sinking mold jacket, then the concrete material is supplied from a stationary supply device situated above the mold and concrete material is dropped from above into an open molding space. Due to the fact that in the device using the sinking mold method the mold jacket is continuously lowered relative to the mold core, the distance between the top end of the mold jacket and the supply device keeps increasing and accordingly there is a growing risk that the falling concrete material splinters to all sides and thus pollutes the parts of the molding machine and impairs the operation.
When the filling of the molding space is completed then the excessive concrete material must have been removed by hand because there has been no possibility to remove it and also to smoothen the upper end of the concrete part by the machine. In the processing of tubular parts by means of a radial pressing device the upper end of the concrete pipe has been shaped by a radial pressing and compacting action which has been found as inadequate. In summary, the following difficulties have been encountered: If it is desired to produce steel concrete pipes there occurs for example the problem that during the filling process the introduced concrete material is catched in the reinforcing wire mesh and immediately compacted whereby cavities can result within the concrete part and a uniform filling and compacting of the concrete material is not guaranteed. When the mold is completely filled up and an additional comptacting is caried out by vibrations then stresses in the reinforcing wire mesh can be caused because the concrete material pulls the wire mesh downwards. Such stresses may lead to the formation of cracks during the subsequent removal of the mold jacket. Moreover, it may happen that the wires at the low side of the reinforcing mesh do not contact the concrete material but form therewith a cavity. Another substantial disadvantage is in that due to circular vibrations of the central vibrator a turning of the reinforcing wire mesh may occur such that further strain develops between the reinforcement and the concrete material in the completed tubular concrete part. This strain may lead to crack formations during the subsequent mold shell removal and in addition, to bending of the concrete parts, for example pipes. When using hydraulic compression with simultaneous vibration of the upper molding ring, the introduced pressing forces can also strain the reinforcing wire mesh which upon the removal of the molding shell are released and again may cause great damage in the finished concrete part.